Steroid pharmaceuticals are a therapeutic agent for various disorders including many inflammatory disorders such as rheumatism and collagen disease, allergic diseases, serious infections and cancer, and they have excellent therapeutic effects on these disorders. However, when they are prescribed for a certain disorder, various actions of steroids are manifested as side effects on normal sites other than lesions to be treated, and as a result a dosage amount may be limited in some cases. In addition, it is easily expected that the longer it remains on a lesion, the more efficacious the steroid would be on the lesion. However, due to the concern regarding the side effect as described above, the number of repeated doses may be also limited. In other words, although the steroids are an excellent pharmaceutical compound which exhibits efficacy in treating various disorders, the use of steroids tends to be avoided at clinical settings due to their side effects. Currently, as an attempt to solve this problem, studies, for example, to accumulate the steroids selectively on a lesion and to release them at the lesion over a long period of time are carried out.
One of such studies relates to a drug delivery system, and as an example of the system, Limethasone (manufactured by Mitsubishi Pharma Corporation), which comprises palmitic acid ester of dexamethasone in a lipid sphere is known in the art (Adv. Drug Delivery Rev., vol. 20, p. 195 (1996)).
Patent Document 1 describes a formulation comprising nano particles of phosphoric acid ester of betamethasone formed with zinc, polylactic acid, and polyethylene glycol-polylactic acid.
Meanwhile, Patent Document 2 discloses a polymer compound comprising a drug bonded to a block copolymer of polyethylene glycol and polyaspartic acid, which forms micelles and has water solubility. Patent Document 3 describes a polymer derivative of camptothecins in which a side chain carboxylic acid group of a block copolymer of polyethylene glycol and polyglutamic acid is bonded to a phenolic hydroxy group of camptothecins. It is known that these polymer compounds accumulate in tumors due to an EPR effect. However, neither Patent Document 2 nor Patent Document 3 discloses a polymer compound to which steroids are bonded.    [Patent Document 1] Japanese Patent Application Laid-open Publication (Kohyo) No. 2006-521367    [Patent Document 2] Japanese Patent Publication No. 2694923    [Patent Document 3] WO 2004/39869    [Non-Patent Document 1] Adv. Drug Delivery Rev., vol. 20, p. 195 (1996)